1. Field of the Invention
The present invention relates to a single-phase semiconductor motor and a fan using the same and, more particularly, to a fan which is used as a small-sized brushless electric fans for refluxing the air in the interior of a car to a temperature sensor of a car air conditioner and as a cooling fan for a personal computer and a computer circuit, and which is also effective as a small-sized fan for locally cooling, and to a single-phase semiconductor electric motor which is effective as a drive source of a light load.
2. Related Art Statement
As the above-described type fan, there is known a fan having an outer diameter of about 30 to 40 mm provided on a rotary shaft of a known DC commutator motor having an outer diameter of 20 mm to 30 mm. There is also known a brushless motor having this structure. A small fan provided at the central portion of an outwardly rotation type rotor so as to make the total apparatus small and flat is disclosed in, for example, U.S. Pat. No. 4,563,622.
Each of the above-described fan motors, however, has the following problems. Firstly, if it is a commutator motor, it includes a mechanically worn portion which makes the durability short, so that it is difficult to have a life of not less than 20,000 hours, which is generally required.
A second problem is that the fan motor generates mechanical noise. If it is used as a conventional brushless motor, the first and second problems are solved, but it brings about a third problem of raised cost and enlargement of the size. Fourthly, if it is formed into a single-phase brushless motor to make it small-sized at a low cost, the efficiency is greatly degenerated.
These problems in the above-described conventional single-phase semiconductor motor are derived from the fact that when it is rotated by an electrical angle of 180 degrees, an excessive rotor current flows at the initial stage and the last stage, especially at the last stage because the counter electromotive force is zero at this time, so that the joule loss which does not contribute to torque is increased, which leads to the lowering of the efficiency.
A technique for preventing this inconvenience is disclosed in U.S. Pat. No. 3,299,335, but in this technique, since it is impossible to effectively utilize all the magnetic fields of the magnet rotor, the coil utilization is reduced by half, the output torque being disadvantageously lowered.
The fan motor disclosed in U.S. Pat. No. 4,563,622 has a fifth problem that since the magnet of the magnet rotor is thin and the torque generated by driving the armature is small, the output torque is small.
A sixth problem of such a fan motor is that it is difficult to be made to have a flat structure except by using the technique in U.S. Pat. No. 4,563,622, and that it is difficult in common to make the diameter of the fan motor small.